At the start of a five-day trip to Latin America, Obama told a joint briefing with Brazilian President Dilma Rousseff Saturday that his visit was a historic opportunity to strengthen U.S. ties with the region's largest economy.

"Brazil's extraordinary rise, Madam President, has captured the attention of the world," he said. "Put simply, the United states doesn't simply recognize Brazil's rise. We support it enthusiastically".

Obama, who is also grappling with deadly crises in Libya and Japan, wants to ensure a bigger U.S. share in Latin America's robust economic growth.

Boosting U.S. exports helps create jobs back home and will aid his 2012 presidential re-election hope. Brazil voiced some discomfort before the visit that Obama was mainly interested in piggy-backing on his host's economic vitality, although he did not dwell on the theme during his public remarks in Brasilia.

Rousseff struck a more confrontational tone, and cited the need for a "relationship of equals" as Brazil's clout in global affairs grows with its economy.

She barely looked at Obama during her remarks, and focused largely on issues that divide the two nations such as trade and the U.S. decision to print money to aid its economic recovery, a move that has hurt Brazil as capital flows make its currency overvalued.

"In the past, our relations were often characterized by empty rhetoric that papered over what was really at stake between us," she said, citing U.S. agricultural subsidies and a tariff on Brazilian ethanol as barriers to be torn down.

"I am equally concerned with the slow pace of the reforms in the multilateral institutions that still reflect an old world," she said.

Brazil believes its greater diplomatic and economic clout have earned it a permanent Security Council seat. Rousseff said this was not about "a minor interest of bureaucratic occupation of spaces," but because she thinks it will produce better results in the search for peace.

In a joint statement, Obama and Rousseff said they recognized the need to reform international institutions to reflect the "current political and economic realities."

But Washington did not explicitly back Brazil's aspirations for a permanent U.N. Security Council seat, as he did for India when visiting New Delhi in November.

"President Obama expressed appreciation for Brazil's aspiration to become a permanent member of the Security Council," the statement said.

OIL AN AVENUE FOR COOPERATION

Overall, Rousseff said she was optimistic about U.S.-Brazil relations, which went through a period of tension last year, and saw opportunities for the two nations to cooperate in developing the South American country's vast new oil fields.

The trip had not been expected to yield major breakthroughs on trade barriers, an area where Washington and Brasilia have been at loggerheads in recent years.

It did, however, produce a series of preliminary agreements aimed at boosting trade and cooperation on issues ranging from space technology to joint development of aviation biofuels.

They also signed an "open skies" agreement that will allow U.S. and Brazilian airlines to fly more routes between each country, as well as a general framework under which the United States would help Brazil prepare for the 2014 World Cup and the 2016 Olympic Games.

Obama's visit is part of an effort to re-engage with neighbors in a region where the United States faces rising competition from China, now Brazil's biggest trade partner.

Obama went ahead with the tour, which also takes him to Chile and El Salvador, even as world powers were seeking to protect civilians from Libyan leader Muammar Gaddafi and as Japan battled a nuclear and humanitarian crisis after a massive earthquake and tsunami.

U.S. officials have said Obama wants to repair diplomatic ties with Brazil under Rousseff, who took office on New Year's Day. Tensions rose under former President Luiz Inacio Lula da Silva over, among other things, Brazil's overtures to Iran. (Additional reporting by Brian Winter and Todd Benson; writing by Stuart Grudgings and Alister Bull; Editing by Paul Simao and Vicki Allen)